But what about other functional outdoor structures, like an entire bridge?

Until recently, 3-D printing has not been used much in civil engineering. In Amsterdam, there is currently a project in the works to 3-D print a steel bridge over a canal. Since it launched in late 2015, however, it has yet to be completed.

But now, a 3-D printed pedestrian bridge that opened in Madrid in December is considered the first innovation of its kind in which civil engineers used the technology on a large scale.

Instead of steel, the bridge is printed in concrete and reinforced with thermoplastic polypropylene. It spans just 12 meters across a small pond in a park in Alcobendas, a city located outside of Madrid.

The Alcobendas bridge was created using parametric design, according to the IAAC news release—a sustainable process that allowed the team “to optimize the distribution of materials and minimize the amount of waste by recycling the raw material during manufacture…challenging the traditional techniques of construction.”

If there is a race to build the first 3-D printed bridge, it looks like IAAC is first across the finish line.

Perhaps 3-D bridges will someday be strong enough to withstand hundreds of cars at rush hour—now that would be a technological achievement.

Watch the video below to see the intricate design of the Alcobendas bridge.